This invention is related to power supplies and more specifically DC-DC converters including the voltage regulator modules (VRMs) used in low voltage power supplies to satisfy the powering requirements of the load such as computer""s microprocessors, low-voltage integrated circuits (ICs), and communication systems.
To satisfy the power supply and dynamic requirements of today""s microprocessors and related communication systems, many approaches have been discussed and proposed. Most of these prior approaches use the compensated feedback loop control system that has a main disadvantage of limited feedback loop bandwidth.
Teachings that are relevant to the background include U.S. Pat. No. 5,278,490 issued January 1994 to Smedley; and, U.S. Pat. No. 5,617,306 issued August 1997 to Lai. Also relevant are publications by: Wenkang Huang, xe2x80x9cA New Control for Multi-phase Buck Converter with Fast Transient Responsexe2x80x9d, IEEE, APEC, Anaheim, Calif., 2001, 273-279; and, K. Smedley and S. Cuk, xe2x80x9cOne-Cycle Control of Switching Converters,xe2x80x9d 22nd Annual IEEE Power Electronics Specialists Conference, Cambridge, Mass., 1991, 888-96.
Single-phase voltage-mode hysteretic control, also called xe2x80x9cbang-bangxe2x80x9d control or ripple regulator control, maintains the output voltage within the hysteresis band centered about an internal reference voltage. If the output voltage reaches or exceeds the reference voltage plus one-half of the hysteresis band, the controller turns OFF the high-side switch, which can be a Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET), and turns ON the low-side switch, to block the energy from being transferred from the input to the output. This latter condition is the power stage OFF-state, and causes the output voltage to decrease. When the output voltage is at or below the level of the reference minus one-half of the hysteresis band, the power stage goes into ON-stage, and the controller turns ON the high-side switch, and turns OFF the low-side switch to allow energy transfer from the input to the output, which causes the output voltage to increase. This hysteretic method of control keeps the output voltage within the hysteresis band around the reference voltage. Thus, an output voltage of one volt is corrected from a deviation as small as a few millivolts as quickly as the output filter allows.
Unlike Pulse-Width Modulation (PWM) controlled power supplies, in the voltage-mode hysteretic control, the output filter design is driven primarily by the need to provide satisfactory output voltage performance in response to fast load transients encountered when supplying power to fast transient loads such as microprocessors. Hence, a smaller output capacitor is needed to provide a smaller transient voltage deviation in the voltage-mode hysteretic control compared to PWM control.
A smaller output inductor filter is desired for fast response but this leads to higher ripple, which means higher switching frequency for the switches in a hysteretic-controlled converter. High switching frequency is desired for faster transient response and smaller converter size (high power density) because of the reduction in the magnetic components size and filter. In a single module, the required switching frequency could reach such a large impractical value that the switching losses are so increased that the the overall efficiency is reduced and provokes excessive heat.
In response to the foregoing, a Multiphase (Interleave) technique is to connect the converters in parallel with phase shift of their control signals to naturally cancel the output current ripple while achieving fast response. The inductor current of the interleaved phases and sum together in a lower ripple output current. This results in a switching frequency for each module that is lower than the output voltage ripple frequency and so a higher output voltage ripple frequency can be achieved as the number of interleaved phases increases. Moreover, the effective output inductance is reduced because of the parallel configuration and hence the transient response is improved. By increasing the number of paralleled phases, higher current capability can be achieved. Thermal problem is also easier to handle in a multiphase converter.
However, when several modules are parallel, it is necessary to keep the total load current equally divided between the modules. This is currently a serious problem which must be overcome in paralleled power supply modules since the asymmetry between the phases and load transients causes the load current not to be equally divided between the modules provoking serious problems such as malfunctioning, heat, slow response, and instabilities.
It is a primary objective of this invention to provide a new control method and control circuit to provide both output voltage regulation for paralleled multiphase power supplies or converters using voltage-mode hysteretic-control.
It is a further objective of this invention to provide a current regulation property of a multiphase converts whereby the load current is equally divided or shared between the paralleled modules.
It is a still further objective of this invention to provide a low voltage power supply with the reduced low output voltage maximum deviation during steady-state and large transients operation, high output current with a high slew rate, fast transient response when the load current switches from approximately zero load to full load and vice versa, high power density, high efficiency, and high reliability.
It is an additional objective of the invention to provide a method for a controller that generates certain control signals derived from an original control signal generated from the output voltage ripple to provide the control for several paralleled converters to achieve hysteretic voltage-mode controlled and interleaved phases.
It is another objective of this invention to provide each module or phase in paralleled modules or phases with the lowest switching frequency possible and the highest possible output voltage ripple frequency whereby the output voltage ripple frequency is optimally equal to the switching frequency of each module multiplied by the number of modules.
It is a further objective of this invention to provide a method and circuit that regulates the current in each power module of phase among a set of paralleled modules or phases to achieve equal current sharing without shortening or changing the control signal (driving signal) ON time (width) and by turning one phase only each cycle to avoid multiple turn ONs within a single cycle.
It is an additional objective of this invention to provide a method and circuit that provides current sharing and regulation by sensing the instantaneous phases currents and finding the phase which carries the smallest current among set of phases to be turned ON when the voltage-mode control loop signal switches from logic low to logic high which makes possible the use of this current regulation or sharing method and circuit with any voltage-mode control method in addition to the multiphase voltage-mode hysteretic control of this invention.
A preferred embodiment of the invention is a multiphase voltage-mode hysteretic-controlled voltage regulator module comprising: an input node; an output node; reference nodes forming a hysteresis band; a feedback control circuit for interleaving two or more power stages with multiphase voltage-mode hysteretic control; and a current sharing circuit to provide equal current sharing for the paralleled multiphase power modules or phases without shortening the ON time of the switches control (driving) signals. The invention is unique in that it includes an independent hysteretic voltage-mode loop and a current sharing loop that provides one phase switch turn ON each cycle and thus avoids mutilple turn ONs in a single cycle.
The preferred method of controlling the voltage and currents in multiphase voltage-mode hysteretic-controlled voltage regulator comprises the steps of: turning ON an upper switch when the output voltage hits the hysteresis boundary or voltage limit (VL); turning ON another upper side switch the next time the output voltage hits the (VL); and so on; and, turning OFF all the upper side switches when the output voltage hits the hysteresis boundary of (VH); and turning ON all the upper side switches when the output voltage hits the boundary or limit. In another method, the phase that carries the smallest current will be turned ON each time the output voltage hits the hysteresis limit VL to regulate the current of each phase.